Botanical/commercial classification: Prunus mahaleb/Mahaleb Rootstock.
Varietal denomination: cv. xe2x80x98UCMH 56xe2x80x99.
Mahaleb rootstocks (i.e., Prunus mahaleb rootstocks) are widely used during both sweet and sour cherry production throughout the world. It has been the common practice to form such rootstock plants from seed following the random outcrossing of parent plants. Accordingly, cherry production encountered when using such plants as an understock has tended to be somewhat variable due to differences in the genotype of the understock. Such variation often has led to reduced field performance on some cherry trees on a random and unpredictable basis. Mahaleb rootstocks in the past have generally been found to be incapable of vegetative propagation on a reliable basis, such as through the use of softwood and hardwood cuttings. Also, such rootstocks in the past have been susceptible to root and crown fungal diseases generally known as Phytophthora spp.
It was an object of my research to provide Prunus mahaleb rootstocks that possess characteristics that overcome shortcomings of the Mahaleb rootstock presently being used during cherry production. More specifically, it was my goal to provide cherry rootstocks that could be vegetatively propagated in an expeditious and reliable manner so that cherry growers can eliminate crop variation that can be traced to lack of uniformity in the rootstock. Also, it was a goal of my research to provide new Mahaleb rootstocks that inherently display needed resistance to disease and thereby make possible a satisfactory cherry crop on a more consistent basis combined with a reduction in the need to replant because of tree loss that is traceable to disease.
The original tree of the new Prunus mahaleb cultivar of the present invention was discovered through detailed evaluation and selection while growing in a cultivated area at the Experimental Orchards at the University of California located at Davis, Calif., U.S.A. The exact parentage of the new cultivar is unknown. The seeds used to form the planting where the discovery took place came from a random collection of wild Prunus mahaleb germplasm that had been collected from around the world. The large number of seedlings present in the planting were carefully studied and evaluated and a single plant possessing the combination of characteristics of the new cultivar of the present invention was selected and was preserved. Had this plant not been discovered and preserved, it would have been lost to mankind.
Other Prunus mahaleb cultivars resulting from the same research are xe2x80x98UCMH 55xe2x80x99 (U.S. Plant patent application Ser. No. 10/028,771, filed concurrently herewith), and xe2x80x98UCMH 59xe2x80x99 (U.S. Plant patent application Ser. No. 10/029,284, filed concurrently herewith).
It was found that the new Prunus mahaleb cultivar of the present invention exhibits the following combination of characteristics:
(a) readily is amenable to vegetative propagation,
(b) performs well as an understock for cherry production,
(c) forms a smaller tree than the xe2x80x98UCMH 55xe2x80x99 cultivar and the standard Mahaleb rootstock,
(d) displays improved resistance to Phytophthora spp. 
(e) makes possible increased xe2x80x98Bingxe2x80x99 sweet cherry scion yield and yield efficiency when compared to the standard Mahaleb rootstock without reduced fruit size,
(f) demonstrates improved precocity in bearing when compared to the standard Mahaleb rootstock, and
(g) produces few suckers.
In view of the above combination of characteristics, the new cultivar of the present invention well meets the needs of cherry producers for use as an improved rootstock. Cherry scion characteristics are no longer influenced by variation in the Mahaleb rootstock resulting from the random outcrossing of parental plants. Also, the disease resistance made possible by the new cultivar is a major advantage for cherry producers.
The new cultivar of the present invention has been repeatedly reproduced through the use of softwood, semi-hardwood, and hardwood cuttings at Davis, Calif., U.S.A. Such propagation has confirmed that the characteristics of the new cultivar are stable and are firmly fixed and are transmitted to subsequent generations on a reliable basis.
The new cultivar of the present invention initially was designated xe2x80x98UC MAHALEB 156-5xe2x80x99, and subsequently has been named xe2x80x98UCMH 56xe2x80x99.